<PAGE>

                                                                   Exhibit 10.11

[LOGO OF ADAPTIVE BROADBAND]



                         ADAPTIVE BROADBAND CORPORATION

                              SEVERANCE AGREEMENT
                              -------------------


THIS SEVERANCE AGREEMENT is entered into as of March 1, 2000 (the  "Effective
Date"), between ADAPTIVE BROADBAND CORPORATION, a Delaware corporation ("ADAP")
and Daniel Scharre (the "Employee").

                                    RECITAL
                                    -------

The Employee serves as ADAP's Executive Vice President and Chief technology
Officer. ADAP and the Employee desire to set forth the terms of the Employee's
severance compensation if the Employee's employment is ended as a result of a
Change in Control.  If a Change in Control occurs, the Employee and other key
employees may be more vulnerable to dismissal or other negative consequences
without regard to the quality of their past or prospective service.  The Board
of Directors (the "Board") believes that it is in the best interest of ADAP and
its stockholders to ensure fair treatment to ADAP's key executives and to reduce
any adverse effects upon their performance that may be caused by the perceived
risks of a merger or acquisition.

The parties agree as follows:

1.  Definitions.  For purposes of this Agreement, the following terms will have
    -----------
    the meanings set forth below.

    1.1  A "Change in Control" will occur if (a) any Person (as defined in
            -----------------
         Section 2(a)(2) of the Securities Act of 1933, as amended) other than
         ADAP, is or becomes the beneficial owner, directly or indirectly
         (including by holding securities which are exercisable for or
         convertible into shares of capital stock of ADAP), of 30% or more of
         the combined voting power of the outstanding shares of capital stock of
         ADAP entitled to vote generally in the election of directors; or, (b)
         ADAP sells, leases or exchanges all or substantially all of its
         property and assets under Section 271 of the General Corporation Law of
         the State of Delaware, or, (c) Continuing Directors cease to constitute
         at least a majority of the Board: or, (d) a majority of the ADAP's
         Outside Directors determine that a Change in Control has occurred.

    1.2  "Continuing Directors" shall mean the directors of ADAP in office on
          --------------------
         January 1, 1999 and any successor to any such director whose
<PAGE>

         nomination or selection was approved by a majority of the directors in
         office at the time of the director's nomination or selection and who is
         not an "affiliate" or "associate" (as defined in Rule 12b-2 under the
         Securities Exchange Act of 1934, as amended) of any person who is the
         beneficial owner, directly or indirectly (including by holding
         securities which are exercisable for or convertible into shares of
         capital stock of ADAP), of 10% or more of the combined voting power of
         the outstanding shares of capital stock of ADAP entitled to vote
         generally in the election of directors.

    1.3  "Disability" means that the Employee has met the qualifications for
          ----------
         ADAP's long-term disability benefit.

    1.4  "Good Reason" includes any of the following:
          -----------

         (a)  the assignment to the Employee of duties inconsistent with, or a
              substantial alteration in the nature or status of, the Employee's
              responsibilities immediately before a Change in Control;

         (b)  a reduction in the Employee's salary or other benefits as in
              effect on the date of a Change in Control;

         (c)  the Employee's relocation to a work site requiring an increase
              in one-way commute from Employee's residence of more than thirty-
              five (35) miles;  or

         (d)  a breach by ADAP of this Agreement if the breach has not been
              cured within 30 days after written notice by the Employee to ADAP
              setting forth with specificity the nature of the breach.

    1.5  "Outside Director" is a member of ADAP's Board of Directors who is
          ----------------
         not, and who during the past six months was not, an employee or
         officer of ADAP.

    1.6  "Termination for Cause" is termination of the Employee's employment
          ---------------------
         as a result of (a) the Employee's willful misconduct or the Employee's
         dishonesty towards, fraud upon, crime against or deliberate or
         attempted injury or bad faith action with respect to ADAP; or (b) the
         Employee's conviction for a felony (whether in connection with ADAP's
         affairs or otherwise).
<PAGE>

    1.7  "Termination Upon a Change in Control" is (a) termination by the
          ------------------------------------
         Employee of Employee's employment for Good Reason within one year after
         the occurrence of a Change in Control; or (b) declination by the
         Employee of an offer of employment from ADAP, or ADAP's successor, for
         Good Reason at the time of a Change in Control if the Employee would
         not have been permitted to remain in Employee's existing position
         following such declination; or (c) termination by ADAP, or ADAP's
         successor, of the Employee's employment within one year after the
         occurrence of a Change in Control other than a Termination for Cause or
         a termination resulting from the Employee's death or Disability.

2.  Term.  If no Change in Control has occurred, this Agreement will expire on
    ----
    December 31, 2001. If a Change in Control occurs prior to December 31, 2001,
    this Agreement will continue in effect, and will not terminate, until either
    the Employee has received the severance compensation provided for below or
    has ceased to be eligible for such compensation by reason of there not
    having been a Termination Upon a Change in Control.

3.  Termination Upon a Change in Control.  If a Termination Upon a Change in
    ------------------------------------
    Control occurs, the Employee will immediately be paid all (a) accrued
    salary, (b) bonus or sales commission compensation equal to the higher of
    (i) the annual bonus or sales commission that would result from implementing
    ADAP's operating plan as approved by the Board during the first quarter of
    the fiscal year during which the Change in Control occurs, provided that the
    criteria which determine the bonus or sales commission payout for such
    fiscal year as of the most recently completed fiscal quarter are equal to or
    exceeding those specified in the operating plan for such period, or (ii) the
    annual bonus, sales commission or other equivalent incentive compensation
    payment established for the Employee by ADAP's successor and based on the
    operating plan of ADAP's successor at the beginning of the bonus's or sales
    commission performance period during which Employee's termination occurs,
    irrespective of the operating performance at the time of termination, (c)
    vested deferred compensation plus the value of any unvested company matching
    shares of ADAP phantom stock in the Supplemental Executive Deferred
    Compensation Plan (other than pension plan or profit sharing plan benefits,
    which will be paid in accordance with the applicable plan), unless the
    Employee is eligible for a delayed payout as authorized by the plan, (d)
    benefits then due under any plans of ADAP or ADAP's successor in which the
    Employee is a participant, (e) accrued Personal Time Off pay or vacation pay
    and (f) reimbursements for any appropriate business expenses incurred by the
    Employee in connection with his duties, all to the date of termination
    ("Accrued Compensation"). Repayment of any existing company loans shall be
    extended if necessary to delay repayment until the beginning of regular
    employment during the period of severance compensation provided for in
    Section 4. The Employee will also be entitled to the severance compensation
    described in Section 4.

4.  Severance Compensation. If a Termination Upon a Change in Control occurs,
    ----------------------
    ADAP or ADAP's successor shall pay weekly severance compensation to the
    Employee for a period
<PAGE>

    ending 104 weeks after termination in an aggregate amount determined by
    adding (a) the Employee's weekly base salary at the time of termination and
    (b) the amount of $553.85 paid in lieu of other employee benefits (including
    health benefits) which the Employee was receiving from ADAP and (c) an
    amount equal to the monthly `Perk Pot' benefit to which the Employee was
    entitled as an officer of ADAP at the time of the Change in Control. If the
    Employee begins regular employment prior to the expiration of the aforesaid
    104 week period, then the severance compensation provided for in this
    Section 4 shall end as of the later of (i) the date of such regular
    employment or (ii) 52 weeks after the Termination Upon a Change in Control.
    Employee agrees to promptly notify in writing the payer of such severance
    compensation if any such regular employment is accepted by the Employee
    during this period and to reimburse the payer for any payments made
    hereunder that cover any period beyond the 52 week minimum during which the
    Employee was a regular employee.

5.  Acceleration of Options.  If a Termination Upon a Change in Control occurs,
    -----------------------
    all stock options held by the Employee immediately before the termination
    will become fully vested and the stock options will be exercisable for the
    periods specified with respect to termination of employment in the plans
    covering the options.

6.  Other Benefits.  Neither this Agreement nor the severance compensation that
    --------------
    it provides for will reduce any amounts otherwise payable, or in any way
    diminish the Employee's rights as an employee of ADAP, whether existing now
    or hereafter, under any benefit, incentive, retirement, stock option, stock
    bonus or stock purchase plan or under any employment agreement or other plan
    or arrangement, provided, however, that the rights granted to the Employee
    and the obligations assumed by ADAP under this Agreement will be in lieu of,
    and not in addition to, any severance or other termination payments to which
    the Employee may be entitled under any employment agreement or other plan or
    arrangement that the Employee may now or hereafter have with ADAP.

7.  Employment Status.  This Agreement does not constitute a contract of
    -----------------
    employment. It does not impose on ADAP any obligation to retain the Employee
    as an employee, to change the status of the Employee's employment or to
    change ADAP's policies regarding termination of employment.

8.  Miscellaneous.
    -------------

    a.   Severability.  If a court or other body of competent jurisdiction
         ------------
         determines that any provision of this Agreement is invalid or
         unenforceable, that provision will be adjusted rather than voided, if
         possible, so that it is enforceable to the maximum extent possible, and
         all other provisions of the Agreement will be deemed valid and
         enforceable to the fullest extent possible.

    b.   Withholding.  Compensation and benefits to the Employee under this
         -----------
         Agreement will be reduced by all federal, state, local and other
         withholdings or similar taxes as required by applicable law.
<PAGE>

    c.   Arbitration.  The parties will submit all controversies, claims and
         -----------
         matters of difference in any way related to this Agreement, its
         performance or breach, to arbitration in San Francisco, California,
         according to the rules and practices of the American Arbitration
         Association from time to time in effect. Any awards in such arbitration
         shall be final and binding on all parties. The arbitrators shall
         allocate the costs of the arbitration in such manner as they deem
         equitable. The arbitrators may require the reimbursement of all or a
         portion of the reasonable legal fees incurred by the prevailing party
         in the arbitration proceeding and any legal proceedings which are taken
         to enforce the arbitral award.

    d.   Entire Agreement: Modifications. (i) This Agreement is the entire
         -------------------------------
         agreement between the parties with respect to the matters covered
         hereby, and may be amended, modified, superseded or canceled, or its
         terms waived, only by a written instrument executed by each party or,
         in the case of a waiver, by the party waiving compliance. (ii) Failure
         of a party at any time to require performance of any provision of this
         Agreement will not affect the right at a later time to enforce the
         same. (iii) No waiver of a breach of this Agreement, whether by conduct
         or otherwise, in any one or more instances will be construed as a
         further or continuing waiver of the breach or of any other term of this
         Agreement. (iv) This Agreement shall inure to the benefit of and be
         binding upon the successors and assigns of the parties hereto.

   e.    Applicable Law. This Agreement will be construed under and governed by
         --------------
         the laws of the State of California without regard or reference to the
         rules of conflicts of law that would require the application of the
         laws of any other jurisdiction.

9.  Prior Severance Agreement.  The Employee and ADAP acknowledge their prior
    -------------------------
    severance agreement dated July 2, 1999. The Employee and ADAP hereby
    terminate such prior severance agreement as of the day immediately prior to
    the Effective Date of this Agreement, and neither the Employee nor ADAP
    shall have any rights or obligations thereunder.


IN WITNESS WHEREOF, the parties have executed this Agreement as of the day and
year first above written.

ADAPTIVE BROADBAND, INC.


____________________________________         __________________________________
Frederick D. Lawrence                        Daniel Scharre
Chairman and Chief Executive Officer         Executive Vice President and Chief
                                             Technology Officer